JERUSALEM (AFP) – The spectre of a military invasion is hanging over the Gaza Strip as militants fired another volley of rockets despite Israeli warnings that failure to stop the attacks would lead to bloodshed.

The latest violence came amid widespread speculation Israeli forces were gearing up for military action in Gaza, which some media said was likely to be a limited operation rather than a full-scale invasion.

“Army preparing for combined ground, air operation in Gaza,” declared the front-page headline in the Haaretz newspaper.

Five rockets and two mortar rounds were fired by militants before dawn, but caused no casualties.

One mortar shell hit a house which was not occupied at the time, near the Kerem Shalom crossing between Israel and the besieged Palestinian territory, causing some damage, residents said.

Violence in and around Gaza has flared since a six-month ceasefire ended on December 19, and escalated dramatically on Wednesday, when militants fired more than 80 rockets and mortar rounds after Israeli forces conducted deadly air strikes over the coastal strip.

Israel responded by tightening the blockade it has imposed since the Islamist Hamas movement, which is branded a terrorist outfit by Israel and the West, violently seized power in Gaza in June 2007.

The Israeli authorities nonetheless opened crossings on Friday to allow the delivery of vital humanitarian aid to the impoverished and overcrowded territory where 1.5 million Palestinians live.

Officials said 80 truckloads of badly-needed supplies were being taken into Gaza.

At the same time, the Israeli government issued dire warnings to Gaza militants, saying the Jewish state would strike back hard if attacks continue.

“I will not hesitate to use Israel’s strength to strike at Hamas and Islamic Jihad,” Prime Minister Ehud Olmert said in an interview with Al-Arabiya television on Thursday, adding ominously: “We have very great and destructive strength which we do not wish to use.”

“I think of the tens of thousands of children and innocents who will be in danger as a result of Hamas’s actions,” he said.

Foreign Minister Tzipi Livni, who hopes to replace Olmert as prime minister after the February 10 election, also vowed Israel would fight back.

“Enough is enough. The situation is going to change,” Livni said in Cairo on Thursday after meeting Egyptian President Hosni Mubarak to discuss the situation in Gaza.

Since the Egyptian-mediated ended last week, Israel has threatened to launch a major offensive on Gaza, and top leaders called for the toppling of Hamas, considered a terrorist group by Israel and the West.

Hamas — which is sworn to the destruction of the Jewish state — has warned in turn that it would retaliate by resuming suicide bombings inside Israel. The last such attack was in January 2005.

Popular pressure for an all-out military operation in Gaza is mounting in Israel.

“The systematic shelling of civilians in Israel’s communities is a war crime and a crime against humanity. The state of Israel has to protect its citizens,” the mass-selling Yediot Aharonot said.

The conservative Jerusalem Post called for the “methodical elimination” of Hamas leaders.

“Once begun, Israel’s battle against Hamas must be terminated only when the Islamists lose their governing capacity,” the English-language newspaper said.